A 10 amp per bank, 3 bank charger is going to pull less than 500 watt's.  That's less than 4 amps on a 120VAC circuit

For a 4 amp circuit, a 100ft drop cord should be 14 gauge.  Some charts will probably say a 50ft cord should also be 14 gauge, but 16 gauge will work just fine for 50ft or less.

Stupid question. But is there such thing as overdoing it in regards to gauge/ft?

 

I ended up getting a 25 ft, 12 gauge cord for when it's being charged inside. 

No. But as a note, if you have one of the lighter gauge extension cords you ought not to use it coiled up as the coiling of the cord adds to the resistance.

20 hours ago, Further North said:

Just an observation: Minn Kota's statement about not using an extension cord is absurd.

And I haven’t been impressed by the robustness of Johnson Outdoors products, lately. You’d expect them to engineer a charger that CAN handle line voltage irregularities well. And don’t get me started about the issues with Humminbird Helix G2 units. . . .

5 hours ago, NorthernBasser said:

Stupid question. But is there such thing as overdoing it in regards to gauge/ft?

No, but the lower the gauge, the heavier and bulkier the cord. I once bought one that was so unwieldy I returned it.

2 hours ago, PECo said:

I haven’t been impressed by the robustness of Johnson Outdoors products, lately. You’d expect them to engineer a charger that CAN handle line voltage irregularities well. And don’t get me started about the issues with Humminbird Helix G2 units. . . . 

I am under the impression that one of their products is designed to deal with that...but I can't recall which one.

 

On the Helix G2s, mine have been fine, but it's small sample and they are both G2N.  A couple folks I know have had issues.

 

Seems that the more complicated we try to get the more issues we have...it also seems like that'd be predictable.

I remember back in the day (1990s), I was on one of my Bass Club's two day tournament road trips.  We were all at a lake side camp ground with 15-20 boat that needed to be changed by a few camp ground electrical outlets.  We all brought long extension cords and three way socket splitters.  I remember six cords plugged into one two socket outlet and there were probably multiple boats plugged into some of those cords.  All of the batteries got charged,  no breakers were thrown,  no fires were started, and no one died.   I guess it was just easier in those days.

15 minutes ago, Tennessee Boy said:

I remember back in the day (1990s), I was on one of my Bass Club's two day tournament road trips.  We were all at a lake side camp ground with 15-20 boat that needed to be changed by a few camp ground electrical outlets.  We all brought long extension cords and three way socket splitters.  I remember six cords plugged into one two socket outlet and there were probably multiple boats plugged into some of those cords.  All of the batteries got charged,  no breakers were thrown,  no fires were started, and no one died.   I guess it was just easier in those days.

This song is fitting, for sure. Give it a listen.